1. Field of the Invention
The present invention relates to a vehicular seat including a forward movable headrest that a headrest moves forward so as to support a head of an occupant when a shock is given to a vehicle.
2. Description of the Related Art
In order to improve the safety of an occupant at the time of a collision from behind, there has been proposed a vehicular seat that a headrest moves forward and supports a head of a seated occupant from a rear side when a shock is given to a vehicle. As disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2000-118280, this type of seat includes a headrest which can move to a front side of a seatback, a shock plate included in a seat back in order to move this headrest forward, and others. When an occupant sitting in a seat is pressed against the shock plate due to application of a shock to a vehicle, the headrest moves forward and a head of the occupant is supported from the rear side.
Like the prior art, since a structure that the headrest is moved forward by utilizing a behavior of an occupant varies depending on physical conditions such as a weight of an occupant or traveling conditions such as a vehicle speed, there is fear that its function cannot be fully demonstrated.
In order to cope with this problem, in a seat apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2003-80985, the headrest is moved forward by a drive force generated by an actuator. This seat apparatus instantaneously moves the headrest forward by the drive force generated by the actuator when a predetermined shock is applied to the vehicle.
In case of incorporating the actuator to the seatback, consideration must be given so as not to deteriorate the comfortableness of the seat. In the seat apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2003-80985, a headrest support frame which can move forward is contained at an upper part of the seat back. The headrest can be supported by this headrest support frame. In a main frame constituting the seat back, an actuator is set at a lower part on an inner surface of a side frame portion on one side. A drive force generated by the actuator is transmitted to the headrest support frame.
The headrest support frame of this seat apparatus is arranged in a dead space (portion which is not brought into contact with the back of an occupant) at the seat back upper part. The actuator is arranged in the dead space along a side frame portion which does not come into contact with the back of an occupant. This seat apparatus requires a transmission mechanism used to transmit a drive force generated by the actuator to the headrest support frame. This transmission mechanism is assembled into a side part of the seat back so as not to deteriorate the comfortableness of the seat.
The actuator is set at a position considerably apart from the headrest support frame. Further, the transmission mechanism also requires conversion of the drive force from the actuator into a force in a movement direction of the headrest. Therefore, this type of transmission mechanism tends to have a large size. Furthermore, the dead space on the seat back side part is a limited narrow area. Therefore, when the relatively large transmission mechanism is set in the dead space, this can be a factor of the uncomfortable feeling when sitting in the seat back.
Further, a long component extending from the actuator to the headrest support frame is used for the transmission mechanism. Such a long component bends upon receiving the drive force from the actuator at the time of a collision of a vehicle, and this can be a factor which delays forward movement of the headrest. Moreover, when such a long component is deformed, it can be considered that a quantity of forward movement of the headrest is decreased. In order to solve this problem, when the rigidity is increased by using a reinforcing member or enlarging a cross section, the transmission mechanism is further increased in size.